Trypanosoma cruzi is the protozoal agent that causes Chagas' disease, an illness that afflicts ten million people in South and Central America and is responsible for considerable human suffering and death. There is no adequate chemotherapy for this disease. We have found that novobiocin, an antibiotic used to treat human bacterial infection in the 1950's, inhibits T. cruzi amastigotes (the only multiplying form of the parasite in infected humans) growing in vitro and inside cultured human fibroblasts at drug concentrations achievable in serum of humans after oral administration. Specific aims of the proposed research are to continue studies on the effectiveness of novobiocin and its analogues in inhibiting T. cruzi grown in the laboratory and to discover the mechanism of inhibition. Investigations of the effectiveness of novobiocin and related compounds as anti-trypanosomal agents are currently proceeding with studies of T. cruzi growing in vitro, within cultured human fibroblasts, and in mice in which untreated infection is fatal. To determine the mechanism of novobiocin inhibition, several experimental approaches will be undertaken. (1) Amastigotes growing in vitro will be examined for drug-induced alterations in parasite structure using electron microscopy and in parasite metabolism following uptake of radioactive precursors into different cellular substituents. (2) Parasites resistant to novobiocin will be selected and characterized. (3) The known target of novobiocin in bacteria is topoisomerase II (DNA gyrase), an enzyme that separates and rejoins DNA circles interlocked like links in a chain. Trypanosomes and related organisms uniquely contain an intracellular structure, the kinetoplast, in which multiple intelocked circles must separate and rejoin as the parasite grows. Thus, structural changes in the kinetoplast and its kDNA after novobiocin treatment will be studied and a trypanosomal topoisomerase II enzyme, a potential target of novobiocin, will be sought. Long term objectives are (1) to identify by screening in vitro and in animal models which of novobiocin and related compounds will be candidates for future drug studies in humans with Chagas' disease; and (2) to determine the target of novobiocin's action on T. cruzi and thereby to define processes essential for trypanosomal growth.